1. Field of the Invention
The present invention relates to the field of optics, and more particularly to a method, a system and a computer program product for assembling an optical module, which includes a light-emitting element and at least one optical component. The method, system and computer program product according to the present invention can be used, for example, to assemble an optical module for exciting an optical amplifier, or for emitting a signal in an optical communication system or network.
2. Discussion of the Background
In the field of optics, it is often desirable to properly align a series of optical components. For example, it may be desirable to maximize the optical coupling between a light source and an optical fiber in an optical communication system so that the output power in the optical fiber 40 is optimized for a given input power of the light source. A series of optical components can be aligned to achieve the desired high optical coupling between the light source and the optical fiber. For example, as shown in FIG. 1A, an emitting end 12 of a light-emitting element 10, e.g., a laser diode (LD) 10, is aligned with a collimating lens 20 and a focusing lens 30 to effectively direct the light from the light-emitting element 10 into an optical fiber 40. When the optical elements are properly aligned, the optical coupling between the laser diode 10 and the optical fiber 40 is maximized, as desired.
To achieve effective optical coupling, the axis of the light emitted from the LD 10 can be positioned perpendicularly to the principal plane of the first lens 20, and the light can be output from the center of the first lens 20 so as to collimate the light without too much scattering (“shading”) of the light. Furthermore, the collimated light output from the first lens 20 can be output from the center of the second lens 30 so that the axis of the focused light is perpendicular to the principal plane of the second lens 30. For the purpose of this document and unless stated otherwise, the axis of a light refers to the straight line passing through the center of the light cross-section as viewed from the direction perpendicular to the traveling direction of the light.
A conventional method for aligning optical elements is shown in FIGS. 2A–B, wherein an LD 10 is aligned with a lens 20 at a desired position so as to obtain effective optical coupling. Referring to FIG. 2A, the light emitted from the LD 10 and output from a first lens 20 is imaged by a camera 50 using a sensor 52 at a first observing position P that faces the LD 10 through the first lens 20. The dimension of the image taken (diameter of the light) and its position on the screen of the camera 50 are determined.
Turning to FIG. 2B, the camera 50 is retracted in a direction perpendicular to the principal plane of the first lens 20 from the first observing position P to a second observing position Q. At the second observing position Q, the dimension of the image of the light output from the first lens 20 (diameter of the light) and its position on the camera screen are determined. The dimension and position of the light determined at the first observing position P is then compared to the dimension and position of the light determined at the second observing position Q. The first lens 20 is moved in the directions perpendicular and parallel to the principal plane thereof so that the dimension and position measured at the observing position P correspond to those measured at the observing position Q. The first lens 20 is thus arranged so that the light output from the first lens 20 is collimated without shading and the axis of the light is perpendicular to the principal plane of the first lens 20. Using a similar method, a second lens 30 (not shown in FIGS. 2A–B) can be arranged so that the axis of the light output from the second lens 30 is perpendicular to the principal plane of the second lens 30.
However, the above conventional method for assembling an optical module by which the light-emitting element 10 is aligned with the optical component 20 presents the following problems.
(1) Because the camera 50 must be moved to image the light output from the lens 20 from at least two observing positions, the method requires additional time to move the camera to the desired positions.
(2) The movement axis of the camera must be aligned with high accuracy to precisely measure the dimension and position of light, which can be difficult.
(3) The brightness of the light entering the camera, and the dimension and shape of the image depend upon the distance between the camera 50 and the emitting end 12 of the LD 10. For example, referring back to FIGS. 2A–B, the optical density at the sensor 52 for the second observing position Q is larger than the optical density at the sensor 52 for the first observing position P. Indeed, as can be seen from FIGS. 2A–B, the cross-section area of the light at the first observing position P is larger than the cross-section area at the second observing position Q. Accordingly, the brightness of the light observed at the first observing position P (FIG. 2A) is lower than the brightness of the light observed at the second observing position Q (FIG. 2B). Such variations in the brightness of light entering the camera, and the dimension and shape of the image degrade measurement accuracy.
(4) Furthermore, in some modules, the LD is tilted so that the orientation of the tilted LD must be modified before positioning a lens. However, the light that has not passed through a lens tends to diverge along its traveling direction according to the diffraction phenomenon. Therefore, the farther a camera is kept from the LD, the smaller the optical density of light entering the camera and the lower the brightness of light entering the camera. The lower brightness of the light can lead to difficulties aligning the LD and a degrading of the measurement accuracy.